Theorem sb4bor 1849

Description: Simplified definition of substitution when variables are distinct, expressed via disjunction. (Contributed by Jim Kingdon, 18-Mar-2018.)

Assertion

Ref	Expression
sb4bor	|- ( A. x x = y \/ A. x ( [ y / x ] ph <-> A. x ( x = y -> ph ) ) )

Proof of Theorem sb4bor

Step	Hyp	Ref	Expression
1		sb4or 1847	. 2 |- ( A. x x = y \/ A. x ( [ y / x ] ph -> A. x ( x = y -> ph ) ) )
2		sb2 1781	. . . . 5 |- ( A. x ( x = y -> ph ) -> [ y / x ] ph )
3		df-bi 117	. . . . . 6 |- ( ( ( [ y / x ] ph <-> A. x ( x = y -> ph ) ) -> ( ( [ y / x ] ph -> A. x ( x = y -> ph ) ) /\ ( A. x ( x = y -> ph ) -> [ y / x ] ph ) ) ) /\ ( ( ( [ y / x ] ph -> A. x ( x = y -> ph ) ) /\ ( A. x ( x = y -> ph ) -> [ y / x ] ph ) ) -> ( [ y / x ] ph <-> A. x ( x = y -> ph ) ) ) )
4	3	simpri 113	. . . . 5 |- ( ( ( [ y / x ] ph -> A. x ( x = y -> ph ) ) /\ ( A. x ( x = y -> ph ) -> [ y / x ] ph ) ) -> ( [ y / x ] ph <-> A. x ( x = y -> ph ) ) )
5	2, 4	mpan2 425	. . . 4 |- ( ( [ y / x ] ph -> A. x ( x = y -> ph ) ) -> ( [ y / x ] ph <-> A. x ( x = y -> ph ) ) )
6	5	alimi 1469	. . 3 |- ( A. x ( [ y / x ] ph -> A. x ( x = y -> ph ) ) -> A. x ( [ y / x ] ph <-> A. x ( x = y -> ph ) ) )
7	6	orim2i 762	. 2 |- ( ( A. x x = y \/ A. x ( [ y / x ] ph -> A. x ( x = y -> ph ) ) ) -> ( A. x x = y \/ A. x ( [ y / x ] ph <-> A. x ( x = y -> ph ) ) ) )
8	1, 7	ax-mp 5	1 |- ( A. x x = y \/ A. x ( [ y / x ] ph <-> A. x ( x = y -> ph ) ) )

Syntax hints:   -> wi 4   /\ wa 104   <-> wb 105   \/ wo 709   A.wal 1362   [wsb 1776

This theorem was proved from axioms:  ax-mp 5  ax-1 6  ax-2 7  ax-ia1 106  ax-ia2 107  ax-ia3 108  ax-io 710  ax-5 1461  ax-7 1462  ax-gen 1463  ax-ie1 1507  ax-ie2 1508  ax-8 1518  ax-10 1519  ax-11 1520  ax-i12 1521  ax-4 1524  ax-17 1540  ax-i9 1544  ax-ial 1548  ax-i5r 1549

This theorem depends on definitions:  df-bi 117  df-nf 1475  df-sb 1777

This theorem is referenced by: (None)